Not sure what kind of traction you'd get with USD here, I've only paid tour guides in greenbacks.
A word of advice though, if you are going to try to use USD, make sure the bills you bring are in pristine condition. They are very very particular here about dollars and if there's a slight tear, pen mark, or blemish no one will take your bill. I've been turned down by banks, cambios, and tour guides for things you wouldn't even notice back in the states.